''While you would not put any one event down to climate change . . . we do know that over time as a result of climate change we are going to see more extreme weather events,'' she said.

Labor frontbencher Peter Garrett said on Wednesday said that Australia could expect more hot days.

"I haven't heard our scientists start to draw a direct connection between the heat we've seen over the last couple of days and climate change," he said.

"But over time I think we can expect to see, consistent with climate predictions, increasing numbers of hot and dry days."

As Fairfax Media reported on Wednesday, the Bureau of Meteorology says this heatwave - in terms of its duration, intensity and extent - is unprecedented in its records.

''Clearly, the climate system is responding to the background warming trend. Everything that happens in the climate system now is taking place on a planet which is a degree hotter than it used to be,'' Bureau of Meteorology's manager of climate monitoring and prediction David Jones said.

As the warming trend increases over coming years, record-breaking heat will become more and more common, he said.

Mr Truss is acting opposition leader as Tony Abbott has been deployed to Nowra, in south-coast NSW, as a volunteer with his local fire brigade.

Mr Abbott has delayed his annual holiday - which was due to start tomorrow - by three days to help the Davidson Rural Fire Brigade.

He spent Wednesday morning at Dean's Gap where he was spotted driving a fire truck.

Mr Abbott has been a volunteer with his local fire brigade since 2000. ''I urge all people living in areas facing fire risk at this time to monitor emergency messages carefully, activate their fire plans and stay safe,'' he said in a statement.

On Wednesday he retweeted a tweet the Opposition Leader sent on Tuesday about the fires - "I'm now on my way to Sydney to be on standby with my local fire brigade" - and added the hashtag "standbystunt".

But Mr O'Connor soon deleted the tweet and apologised: "Apologies for any offence. I respect and acknowledge the critical work of all our volunteer firefighters including Tony Abbott."

But Mr O'Connor has received some support from Brisbane Labor MP, Graham Perrett. "We all love his [Mr Abbott's] volunteering but [it's] when we see it through the prism of his press release that the queries start," Mr Perrett said.

Mr O'Connor is on leave and his office said he was not able to comment.

Early on Wednesday morning, Mr Abbott issued a short media statement about his volunteering plans for the week.

Coalition MP Joanna Gash, who is also the Mayor of the Shoalhaven City Council (which takes in the Nowra area), said Mr Abbott did not want any recognition or media attention for his firefighting.

"We are lucky to have him on board to help with our own crews and the number of other volunteers we have on site," Ms Gash told ABC TV.

"I hardly recognised him this morning in his clobber."

Also on Wednesday, Ms Gillard tweeted her thanks to those helping fight the fires: ''Our thanks go to firefighters, police, SES and everyone fighting the fires. You've worked a miracle keeping so many people and homes safe.''